more docs

extensions/elasticsearch/README.md

@@ -67,10 +67,29 @@ The following is an example model called `Customer`:
 ```php
 class Customer extends \yii\elasticsearch\ActiveRecord
 {
+    /**
+     * @return array the list of attributes for this record
+     */
     public function attributes()
     {
         return ['id', 'name', 'address', 'registration_date'];
     }
+
+    /**
+     * @return ActiveRelation defines a relation to the Order record (can be in other database, e.g. redis or sql)
+     */
+    public function getOrders()
+    {
+        return $this->hasMany(Order::className(), ['customer_id' => 'id'])->orderBy('id');
+    }
+
+    /**
+     * Defines a scope that modifies the `$query` to return only active(status = 1) customers
+     */
+    public static function active($query)
+    {
+        $query->andWhere(array('status' => 1));
+    }
 }
 ```
 
@@ -90,3 +109,19 @@ It supports the same interface and features except the following limitations and
 - As elasticsearch is a data storage and search engine there is of course support added for search your records.
   TBD ...
 - It is also possible to define relations from elasticsearch ActiveRecords to normal ActiveRecord classes and vice versa.
+
+Elasticsearch separates primary key from attributes. You need to set the `id` property of the record to set its primary key.
+
+Usage example:
+
+```php
+$customer = new Customer();
+$customer->id = 1;
+$customer->attributes = ['name' => 'test'];
+$customer->save();
+
+$customer = Customer::get(1); // get a record by pk
+$customers = Customer::get([1,2,3]); // get a records multiple by pk
+$customer = Customer::find()->where(['name' => 'test'])->one(); // find by query
+$customer = Customer::find()->active()->all(); // find all by query (using the `active` scope)
+```
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